1. Field of the Invention
The present invention relates to a display device, and more particularly, to an electro-luminescent device and a method for manufacturing the same.
2. Discussion of the Related Art
Recently, the display industry has flourished with the introduction of TFT-LCDs to the TV market, the growth of plasma display panel (PDP) TVs, the advent of next-generation displays such as organic electro-luminescent (EL) devices, and the like. In particular, the advent of diverse displays has been mainly concentrated on application to TVs and mobile equipment, thereby enabling consumers to select desired displays among a wide variety of displays. Also, it is expected that the advent of an inorganic EL device, the driving principle of which is similar to that of organic EL devices, will provide consumers with an opportunity to select another display in the future, even though such an inorganic EL device is still a nascent technology and has yet to enter the market.
Organic EL devices, as developed recently, have been used since 2002 for consumer goods such as displays for mobile phones. However, inorganic EL devices have yet to be widely recognized for consumer applications. Although inorganic EL devices are different from organic EL devices in terms of the manufacturing processes and whether the luminous material is an organic material or an inorganic material, inorganic EL devices have the same driving mechanism (using an electric field) as organic EL devices.
However, inorganic EL devices are improper for miniature devices (for example, mobile equipment) because inorganic EL devices involve electrical shock danger due to their high driving voltage in contrast to organic EL devices. On the other hand, inorganic EL devices have an advantage in larger displays because thin film transistors (TFTs) are unnecessary. In addition, inorganic EL devices are similar to PDPs in terms of the driving system because high driving voltages for luminescence of the inorganic material is necessary.
As compared to other displays, inorganic EL devices have remarkable advantages of low costs according to their simple manufacturing processes and of stable performance even in harsh environments. The inorganic EL devices also have a great advantage in that products can be manufactured using an inexpensive thin film process, as compared to TFT-LCDs and organic EL devices which require the use of thin film processes.
FIG. 1 is a circuit diagram schematically illustrating a general EL panel. As shown in FIG. 1, the EL panel includes gate lines GL1 to GLm and data lines DL1 to DLn which are arranged on a glass substrate 10 intersecting with each other. The EL panel also includes pixel elements PE each arranged at an intersection between each of the gate lines GL1 to GLm and each of the data lines DL1 to DLn.
Each pixel element PE is activated when a gate signal on an associated one of the gate lines GL1 to GLm is enabled. In the activated state, the pixel element PE emits light with an intensity corresponding to the level of a pixel signal on an associated one of the data lines DL1 to DLn.
To drive the EL panel, a gate driver 12 is connected to the gate lines GL1 to GLm, and a data driver 14 is connected to the data lines DL1 to DLn. The gate driver 12 sequentially activates the gate lines GL1 to GLm. The data driver 14 supplies pixel signals to the pixel elements PE via the data lines DL1 to DLn, respectively.
The pixel elements PE, which are driven by the gate drivers 12 and data drivers 14, will now be described. FIG. 2 is a circuit diagram illustrating one pixel element in the EL panel of FIG. 1.
As shown in FIG. 2, the pixel element includes an EL cell OLED having a cathode terminal connected to the ground, and a cell driving circuit 16 adapted to drive the EL cell OLED in accordance with a signal on a gate line GL and a signal on a data line DL. The EL cell driving circuit 16 includes a first PMOS TFT T1 adapted to perform a switching operation for the data signal on the data line DL in accordance with the signal on the gate line GL, and a second PMOS TFT T2 adapted to supply a voltage to the EL cell OLED in accordance with the data signal on the data line DL. The EL cell driving circuit 16 also includes a storage capacitor Cst connected between gate and source terminals of the second PMOS TFT T2 to maintain the data signal received via the first PMOS TFT T1 for a predetermined time.
Hereinafter, a related art method for manufacturing an EL device will be described with reference to the drawings. FIGS. 3A to 3E are sectional views illustrating processing steps of the related art EL device manufacturing method.
As shown in FIG. 3A, first electrodes 22 are first formed on a transparent substrate 21 such that the first electrodes 22 are uniformly spaced apart from one another in a column direction, using a method in which an organic material containing metal grains is printed on the transparent substrate 21. Here, each first electrode 22 is a reflective electrode made of Al exhibiting excellent reflectivity.
Thereafter, as shown in FIG. 3B, an insulating film 23 is formed over the entire surface of the transparent substrate 21 such that a predetermined portion of each first electrode 22 at one side of the first electrode 22 is exposed. The first electrodes 22 exposed through the insulating film 23 function as first pad terminals, respectively.
As shown in FIG. 3C, a phosphor layer 24 is then formed on the insulating film 23 in accordance with a sputtering method under the condition in which a shadow mask (not shown) is used. For the phosphor layer 24, a blue phosphor layer may be used.
Subsequently, as shown in FIG. 3D, transparent metal (for example, indium tin oxide (ITO) or the like) is deposited over the entire surface of the transparent substrate 21 including the phosphor layer 24 in accordance with a sputtering method. The transparent metal deposited in accordance with the sputtering method is then selectively removed using a laser ablation technique, to form a plurality of second electrodes 25 uniformly spaced apart from one another in a row direction perpendicular to the first electrodes 22. The second electrodes 25 function as transparent electrodes, respectively. The second electrode 25, which is arranged at one outermost portion of the substrate 21 corresponding to the side of the first pad terminals, is a second pad terminal.
Thereafter, red (R), green (G), and blue (B) color representing layers 26 are formed around the second electrodes 25, as shown in FIG. 3E. A protective film (not shown) is formed over the entire surface of the resulting structure of the EL device obtained in accordance with the above-mentioned processes, to protect the EL device. After performing a sealing process, the EL device is connected to driving circuits or chips via the first and second pad terminals, using TCPs. That is, the EL device is connected to a gate driver and a data driver to receive signals from the drive, thereby displaying an image.
However, the above-mentioned related art EL device manufacturing method has various problems. That is, first, the phosphor layer may be damaged when the transparent metal layer is deposited over the phosphor layer and is then selectively removed to form the second electrodes (transparent electrodes). As a result, the throughput may be degraded. Second, addition of a function to reduce the damage is necessary. Furthermore, the second electrodes are formed using laser ablation because the phosphor layer exhibits poor resistance to wet etching. For this reason, the utility of existing LCD manufacturing equipment is degraded.